Circuit interrupting means for high-voltage direct current

ABSTRACT

A high voltage direct current interrupting arrangement consists of two electrical switches connected in series. One of the switching devices is a commutating circuit breaker which is connected in parallel with a series connection of a capacitor and a spark gap. A surge diverter is also connected in parallel with the commutating circuit breaker. The surge diverter takes over the current and breaks it during a breaking operation whereafter the other switching device is opened to isolate the circuit.

Brown et a1. 317/11 E Unlte States Patent 11 1 1111 3,809,959

Pucher May 7, 1974 CIRCUIT INTERRUPTING MEANS FOR 3,246,206 4/1966 Chowdhuri 317/16 x GH VO DIRECT CU 3,566,197 2/1971 Nilsson 317/31 2,208,399 7/1940 Slepian 317/11 E [75] Inventor: Walter Pucher, Vasteras, Sweden [73] Assignee: Allmanna Svenka Elektriska Primary Examiner-Robert K. Schaefer -Aktiebolaget,'Vasteras, Sweden Assistant Examiner-William J. Smith [22] Filed: Mar. 14, 1973 [21] Appl. No, 341,059 ABSTRACT A high voltage direct current interrupting arrange- 301 F ig A li i P i i D ment consists of two electrical switches connected in Mar 21 1972 Sweden 3619/72 series. One of the switching devices is a commutating circuit breaker which is connected in parallel with a 52 US. Cl. 317/11 E 317/11 (3 307/136 Series COmeCtiO of a capacit" and a Spark A [51 1111. C1. 110211 7/22 Surge divert is also Onnected Parallel with the of s 1 l E commutating circuit breaker. The surge diverter takes over the current 'and breaks it during a breaking oper- [56] References Cited ation whereafter the other switching device is opened UNITED STATES PATENTS to Solate 3,381,175 4/ 1968 5 Claims, 1 Drawing Figure CIRCUIT INTERRUPTING MEANS FOR HIGH-VOLTAGE DIRECT CURRENT BACKGROUND OF THE INVENTION 7 1. Field of the Invention The present invention relates to a means for interrupting'high-voltage direct current. The circuit interrupting means is preferably intended to be used as a load switch, that is, a switch for interrupting current during normal operation, but with special dimensioning it may also be used for interrupting short-circuit currents.

2. The Prior Art For interrupting high-voltage direct current circuits interrupting means of the above kind are known previously, in which a circuit breaker is used for commutating the current from the main current path to an energy absorbing parallel resistor (Elektrotechnische Zeitschrift, Ausg. A, 1968, No. 19. pp. 42l-423). In these known means the residual current through the resistor is interrupted with the help of a series-connected d-c circuit breaker of a special design, which is connected in parallel with means for overvoltage protection consisting, for example, of a series-connection of a resistor, a capacitor and a spark gap. It is true that this circuit breaker for residual current does not have to interrupt very high current, but it must be constructed to interrupt at full line voltage. Such special d-c circuit breakers involve expensive constructions and high development costs.

SUMMARY OF THE INVENTION The object of the present invention is to provide a circuit interrupting means for high-voltage direct current, which, to the greatest possible extent, is built up of a-c devicesalready in existence. This is achieved by having a switch arranged in parallel with a series connection of a capacitor and a spark gap and with a surge diverter, this unit being in series, with a second switch. The surge diverter takes over the current and breaks it upon a breaking operation whereupon the second switch is opened to isolate the circuit. A device of this design shows both lower cost of production and lower cost of development than the previously known circuit interrupting means for the same purpose.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will be further described with reference to the accompanyingdrawing, which shows, as an example, a diagram for a circuit interrupting means according to the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENT The circuit interrupting means shown comprises equipment for commutating, interrupting and insulating. The equipment for commutating consists of a socalled commutating circuit breaker 1 which is connected in parallel with a capacitor 2 through a'spark gap 3. The equipment for interrupting consists of a surge diverter 4, and the equipment for insulating con sists of an isolator 5.

During a breaking operation the circuit breaker l is opened, said circuit breaker thus generatingan arc voltage which ignites the spark gap 3. In this way, the current is rapidly transmitted to the capacitor 2, the are in the circuit breaker 1 thus becoming extinguished. When the voltage across the capacitor has reached the ignition level of the surge diverter 4, the latter is ignited, takes over the current and forces it in a controlled manner towards zero, that is, it interrupts the current without giving rise to unallowable overvoltages. When the current is interrupted, the isolator 5 opens and isolates the circuit.

The proposed circuit interrupting means differs from other commutating interrupting means by placing the function of interruption wholly on the surge diverter 4, whereas the purpose of the other components 1, 2 and 3 is only to activate the diverter and transmit the current to said diverter. In this way, the device can be built up from a relatively small number of components which, moreover, do not involve exceptionally high expense.

The surge diverter 4 consists of a resistor, preferably of voltage-depending type, connected in series with a self-extinguishing spark gap. A design of such a surge diverter which is suitable for the purpose is described in U.S. Pat. No. 3,566,197. Such a surge diverter consists-of a plurality of branches connected in parallel and comprising non-linear resistors and spark gaps providing arc extension by magnetic blow-out coils, and cross-impedances arranged between the branches for controlled transmission of ignition pulses between the branches. The surge diverter branches and the crossimpedances are so dimensioned and arranged that a permanent ignition and extinguishing of the arc takes place in all branches, so that the current is permanently moved from one branch to another until it is finally interrupted. Surge diverters of this type with the required breaking capacity are available on the market. Only a special adaption of the discharge voltage to the purpose in question is required, so that the recovery voltage after extinguishing does not exceed the spark-over voltage of the diverter, that is, does not ignite the diverter anew.

A conventional a-c circuit breaker of low oil content type (with the required number of breaking elements) may be advantageously used as commutating circuit breaker, since this type of circuit breaker has proved to be able to build up a relatively high are voltage. In addition to this, it is possible to derive advantage from the very rapid rebuilding of the dielectric strength, typical of breaking gaps in oil, when the arc is extinguished.

The isolator 5 should be high-speed-operated and arranged to open simultaneously with or immediately after the opening of the commutating circuit breaker 1. In this way, the required insulating distance across the circuit interrupting means is rapidly achieved, and the risk of external overvoltages causing restrike or flashover in any of the components 2, 3 and 4 is eliminated, said components being suitably designed for a relatively low insulating level in order to reduce the cost.

diverter 4 direct in parallel with the capacitor 2, even if such a design would involve a somewhat greater strain on the spark gap 3 than in the design shown in the drawing. Further, the circuit breakers l and 5 do not necessarily have to consist of separate switching devices of different designs, but these circuit breakers could be built together to one unit containing breaking elements of one and the same type.

I claim:

1. A device for interrupting high-voltage direct current comprising first and second electrical switching devices (1,5) connected in series, the first switching device (l) constituting a commutating circuit breaker, a series connection of a spark gap (3) and a capacitor (2) connected in parallel with the first switching device (1), and a surge diverter (4) connected in parallel with said first switching device, whereby said surge diverter takes over the current upon opening of said firstswitching device to break the current, whereupon said second switching device is opened.

2. A device as claimed in claim 1, wherein the comnected in parallel and comprising non-linear resistors and spark gaps providing arc extension by magnetic blow-out coils, and cross-impedances arranged between the branches for. controlled transmission of ignition pulses between the branches.

5. A device as claimed in claim 4, wherein the surge diverter branches and the cross-impedances are so dimensioned and arranged that a permanent ignition and extinguishing of the arc takes place in all branches, so that the current is permanently moved from one branch to another until it is finally interrupted. 

1. A device for interrupting high-voltage direct current comprising first and seCond electrical switching devices (1,5) connected in series, the first switching device (1) constituting a commutating circuit breaker, a series connection of a spark gap (3) and a capacitor (2) connected in parallel with the first switching device (1), and a surge diverter (4) connected in parallel with said first switching device, whereby said surge diverter takes over the current upon opening of said first switching device to break the current, whereupon said second switching device is opened.
 2. A device as claimed in claim 1, wherein the commutating circuit breaker (1) is a circuit breaker of low liquid content type.
 3. A device as claimed in claim 1, wherein the second switching device (5) is a high-speed isolator.
 4. A device as claimed in claim 1, wherein the surge diverter (4) comprises a plurality of branches connected in parallel and comprising non-linear resistors and spark gaps providing arc extension by magnetic blow-out coils, and cross-impedances arranged between the branches for controlled transmission of ignition pulses between the branches.
 5. A device as claimed in claim 4, wherein the surge diverter branches and the cross-impedances are so dimensioned and arranged that a permanent ignition and extinguishing of the arc takes place in all branches, so that the current is permanently moved from one branch to another until it is finally interrupted. 